The processes for the measurement of the angular position of a target by a monopulse radar are based on the comparison of two or more different radiation diagrams pointed at the same target. There can be one or more measurements, e.g. one in elevation and one in azimuth.
The angular measurements are calculated on the basis of the amplitude of an electrical signal which is representative of the measurement. These measurements suffer from noise, particularly modulation noise resulting on the one hand from movements of the target relative to the radar and on the other hand from the geometry of the target. This noise limits the performances of radar systems and particularly of automatic tracking systems.
A radar system having means for measuring angular position or deviation has at least two radiation diagrams or patterns on reception. These diagrams are generated in at least two reception channels which respectively supply signal .SIGMA. and a difference signal .DELTA. (or two separate difference signals .DELTA.S and .DELTA.G if the measurements are performed in elevation and azimuth. The angular measurement generally utilizes the quotient .epsilon. of the signals .DELTA. and .SIGMA.. The quotient .epsilon. is a measurement of the off-boresight angle of the detected target, i.e. of its offset from the axis of the two radiation diagrams. Filtering of the angular-measurement noise can be carried out by means of simple linear or nonlinear filters. Linear filtering has the disadvantage of leading to significant measuring delays in the case of deviation measurements. These delays then lead to dynamic errors in the measurement of the relative position of the detected target or targets. Nonlinear filtering has led to improvements which, however, have been found to be inadequate in certain cases. A nonlinear filtering device disclosed in commonly owned U.S. Pat. No. 4,220,953 (granted to one of us, Roland Carre) measures the deviation signal .epsilon. at instants of minimum error probability as determined from the magnitude of the sum signal .SIGMA. and possibly of an ancillary deviation signal .epsilon.q in quadrature with signal .epsilon.. However, the residual noise levels and the measuring delay are still by no means negligible. Thus, these filters have a reduced efficiency in automatic tracking systems when using rapidly maneuvered targets, whereby the target geometry can vary rapidly in view of the movement of the latter.